[WZX]

Hello, friends！

I use CFD simulation to study the hydrogen production by Methanol-Steam Reforming Reaction (MSRR). The overall reactions of MSRR can be written as follows:

The reaction rate expressions for these overall reactions involved in the
process of methanol-steam reforming are as follows：

Parameters of the comprehensive kinetic model of the methanol-steam reforming reaction process

And these three reaction rates can be implemented by a UDF of DEFINE_VR_RATE(MSR_rate,c,t,r,mw,yi,rr,rr_t ). However, when I was editing the code, I encountered the following difficulties:
a)In the formula, the partial pressure of each gas component is used, but in DEFINE_VR_RATE, there is only the mass fraction yi, so I want to get the mole fractionXi through the mass fraction, and then multiply it by the total pressure to get the partial pressure of each component.Is this thinking right?And how to express the total pressure?C_P(C,t)？
b) In the formula, the denominator contains the partial pressure of products such as H2 and CO. however, my import condition gives the mass fraction of reactant CH3OH & H2, which leads to the fact that the denominator is 0 at the beginning and cannot operate. How can I solve this problem?
Can anyone help me